It has been suggested in British Pat. No. 788,855 that mandelonitrile-.beta.-D-glucuronic acid may be used in the treatment of malignant tumors as .beta.-glucuronidase is prevalent in malignant tissues and this enzyme will selectively attack mandelonitrile-.beta.-D-glucuronic acid at the site of the malignant tumors to split off hydrogen cyanide. U.S. Pat. No. 2,985,664 is also related to mandelonitrile-.beta.-D-glucuronic acid and a method of producing same.
It has been discovered, however, that none of the methods of producing this compound set forth in the above mentioned patents are reproducible. Attempts to oxidize prunisin by the methods described by Krebs produce the glucuronide of mandelic acid because the CN group is unstable. Attempts to condense mandelonitrile with glucuronic acid or glucuronolactone or tetraacetylglucuronolactone halogenide have failed because the mandelonitrile tends to polymerize.
In 1966, Merck Pharmaceutical Company was requested by the U.S. National Institutes of Health to duplicate the synthesis of this compound as taught by the Krebs patents. In a series of quarterly progress reports to the Cancer Chemotherapy National Service Center, Merck, Sharpe & Dohme Research Laboratories reported that none of the methods disclosed in either of the above mentioned Krebs patents could be duplicated. The Merck reports specified that while amygdalin can be hydrolyzed to mandelonitrile-.beta.-D-glucoside (although by acid hydrolysis rather than enzymatic hydrolysis), none of the desired material could be obtained from catalytic air oxidation of the glucoside as taught by the Krebs patents. They were further unable to repeat the Krebs directions for total synthesis by condensing d,l-mandelonitrile with .beta.-glucuronic acid.
The Merck report details many unsuccessful efforts which were made to oxidize the mandelonitrile-.beta.-D-glucoside to the corresponding mandelonitrile-.beta.-D-glucuronic acid. It has specified, however, that the formation of any detectable amount of the desired product was never demonstrated in spite of many variations in conditions and catalysts either using Krebs recommended catalyst, "platinum black," or other catalysts, including platinum or palladium on charcoal, platinum oxide, Adam's catalyst, or certain specially prepared sugar oxidation catalysts.
The Merck report also reported on attempted chemical oxidation of the glucoside to the glucuronic acid by first preparing the 6-trityl derivative of the glucoside followed by acetylation and removal of the 6-trityl-group in refluxing 80% aqueous acetic acid. It is reported that several chemical oxidation agents, such as potassium permanganate and chromic acid were tried giving a dark oily product, from which no useful material was obtained. It was further reported that catalytic air oxidation on this triacetate also gave back the starting material.
The only method discovered by Merck to be even partially successful in producing the desired glucuronic acid entailed oxidation with liquid nitrogen dioxide of the unprotected monoglucoside. The results were so poor however, that only a 6.5% yield could be obtained (less than 0.5 g) after several recrystallizations.
Fenselau et al in Science, 198 (4317) 625-627, 1977, reported that no successful synthesis of mandelonitrile glucuronide has been reported since the original Krebs patents. Furthermore, they report that since the original Krebs processes had not been reproduced, they proceeded to develop their own synthesis of mandelonitrile glucuronide using UDP-glucuronosyl transferase immobilized on beaded Sepharose.
In PCT application WO 80/00791 a method of synthesis of mandelonitrile-.beta.-D-glucuronic acid was described which comprises first reacting mandelic acid with gaseous ammonia to form a reaction product, and then reacting with the methyl (tri-O-acetyl .beta.-D-glucopyranosyl) bromide uronate to produce methyl ester of the corresponding glucuronic acid. This compound may then be mixed with acetic anhydride to convert the mandelic acid-ammonia reaction product to mandelonitrile. Treatment with barium hydroxide and sulfuric acid will then produce the mandelonitrile-.beta.-D-glucuronic acid. However, this method has a yield of only about 30%.
It is thus clear that the synthesis of mandelonitrile-.beta.-D-glucuronic acid has been very difficult and cannot be accomplished by conventional techniques in any kind of a desirable yield.
PCT international publication WO 80/00791, the entire contents of which are hereby incorporated by reference, discloses significant utilities for mandelonitrile-.beta.-D-glucuronic acid including antibacterial activity against bacterial infections by bacteria which are known to have high .beta.-glucuronidase activity and against certain tumors which have high .beta.-glucuronidase activity.